EEEB413_exam_sem2_1011

EEEB413, Semester II 2010/2011

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COLLEGE OF ENGINEERING

PUTRAJAYA CAMPUS

FINAL EXAMINATION

SEMESTER 2 2010 / 2011

PROGRAM : BACHELOR IN MECHANICAL ENGINEERING (Hons.)

PROGRAM

MATAPELAJARAN : ELECTRO-MECHANICAL SYSTEMS

SUBJECT

KOD MATAPELAJARAN : EEEB413

SUBJECT CODE

TARIKH : MARCH 2011

DATE

MASA : 3 HOURS

TIME

Instructions to candidates:

1. Answer ALL questions.

2. Total number of questions in this booklet: FIVE (5)

3. This is a close book examination. Usage of scientific calculator is allowed.

4. All answers and rough work must be done in the examination answer booklet.

5. Useful equations are provided at the last page of this booklet.

DO NOT OPEN THIS QUESTION PAPER UNTIL YOU ARE INSTRUCTED TO DO SO

THIS QUESTION PAPER CONSISTS OF 13 PRINTED PAGES INCLUDING THIS

COVER PAGE.


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QUESTION 1 [20 marks]

a) List 5 important steps in motor sizing and selection process. (5 marks)

b) List 3 effects that govern operation of motors, generators and transformers.

(3 marks)

c) Give 2 methods used to control the speed of an induction motor. (2 marks)

d) Give 2 advantages of 3 phase system compared to single phase system in power

transmission. (2marks)

e) What is the function of commutator and brush in DC machine? (2 marks)

f) Name 2 types of brushed DC motor. (2 marks)

g) Explain how a stepper motor works (rotating magnetic field and rotor). (4 marks)

[5+3+2+2+2+2+4=20 marks]

End of Question 1


A 208V, 45kVA, 0.8PF leading, 60Hz, Δ-connected synchronous motor has a negligible

armature resistance of and synchronous reactance of Xs= 2.5Ω. It’s friction and windage

losses are 1.5kW, and its core losses are 1.0kW. Initially, the shaft is supplying a 15hp

load, and the motor’s power factor is 0.8 leading.

a) Sketch the phasor diagram of this motor and find the values of IA, IL and EA.

(10 marks)

b) Assume that the shaft load is now increased to 30hp. Find the IA, IL and EA after

the load change. What is the new power factor? (10 marks)

[10+10=20 marks]

End of Question 2


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A 208V three phase power system is shown in Figure 2 above. It consists of an ideal

208V three-phase generator connected through a three-phase transmission line to a load.

The transmission line has an impedance of 0.06+j0.12Ω per phase, and the load has an

impedance of 4+j3Ω per phase. For this simple power system, find

a) The magnitude of the line current ( LI ). (4 marks)

b) The magnitude of the load’s line-to-line voltage ( LLV ) and phase voltage ( LV ).

(4 marks)

c) The real, reactive and apparent powers consumed by the load. (3 marks)

d) The real, reactive and apparent powers consumed by the line AND supplied

by the generator. (6 marks)

e) Power factor for both the load and the generator. (3 marks)

[4+4+3+6+3=20 marks]

End of Question 3

Figure 2

+_

+_

+ _

0.06Ω

0.06Ω

0.06Ω

j0.12Ω

j0.12Ω

j0.12Ω

V

LZ LZ

LZ

LZ = 4+j3 208V

_

+


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A 15-hp, 208V, 50Hz, Y-connected induction motor has the following parameters:

1R = 0.220Ω 2R = 0.127Ω MX = 15Ω

1X = 0.430Ω 2X = 0.430Ω

If the motor is operating at an induced torque of 100 N-m with a synchronous speed of

1500 rpm, determine the following.

a) The stator current of the motor, in term of slip (s). (5 marks)

b) The air gap power ( AGP ) and the slip of the motor. (5 marks)

c) The operating speed of the motor. Justify your answer. (4 marks)

d) The converted power ( convP ) and the power loss in the rotor ( RCLP ). (4 marks)

e) What will happen if the rotor speed becomes larger than the synchronous

speed? (2 marks)

[5+5+4+4+2=20 marks]

End of Question 4


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Company A is designing a tabletop moving vertically on a ball screw for its production

line. The motor that drives the tabletop has to be selected to fulfill the requirements above.

4-pole single phase induction motor is thought to be suitable for the system. Based on

the requirements and the catalog provided in Appendix A, select the appropriate motor.

Justify your answer. Note that no-load speed is approximately 1750 rpm and rated speed

is between 1450 rpm to 1550 rpm for a 4-pole motor at 60 Hz. Use safety factor of 2 and

select a pinion shaft, lead wire type motor.

[20 marks]

End of Question 5

-END OF QUESTION PAPER-

Total mass of table and work, m1 = 30 kg

Table speed, V = 15 ± 2 mm/s

External force, FA = 0N

Ball screw tilt angle, = 90

Total length of ball screw, LB = 800mm

Ball screw shaft diameter, DB = 20mm

Ball screw pitch, PB = 5mm

Ball screw lead, A = 5mm

Ball screw efficiency, = 0.9

Material of ball screw is iron (density =7.9x103kg/m

3

Internal frictional coefficient of pilot pressure nut, 0 = 0.3

Friction coefficient of sliding surface, = 0.05

Motor power supply, Single phase 110 V, 60 Hz

Movement time, intermittent operation, 5 hours per day

-Load with repeated starts and stops

-Required load holding

Required specifications and structural specifications


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LIST OF EQUATIONS

22

1 746

120

sync m

sync

F R Ni Hl

lR

A

F Bil

e Blv

P

VP I R

R

hp W

fen

p

n ns

n

1

1

1

3

3

3

cos

sin

3 3

3 cos 3 cos

3 sin 3 sin

3sin

3sin

A

A

A

A T L

A T L

A T L

A

s

A

m s

S V I

P V I

Q V I

S V I V I

P V I V I

Q V I V I

V EP

X

V E

X

1

22 2

122 12

2

1

2

2max max

2 22 22 2

3,

3

2

TH

mTH

m

mind TH

m

sync TH TH

TH

TH

TH TH sync TH TH TH

XV V

X X

RV Xs where R R

X XRR X X

s X X

R Vs

R X X R R X X

I

VZ


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Tabletop speed,

APPENDIX A

EEEB413_exam_sem2_1011

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